Variable-Rate Chemigation via Center Pivots

Abstract

Center pivots can be used to achieve variable-rate chemigation—applying spatially variable dosages of agricultural chemicals within the same field. This paper first presents equations specifying how a center pivot and the associated chemical injection pump can be operated to vary chemical dosages among sectors of a circle or among arc-shaped zones. This paper then introduces a software tool that facilitates computations for variable-rate chemigation. This paper finally documents two field tests of commercial, uncustomized variable rate chemigation systems. In the catch can test, mean absolute relative error in zone-average adjusted chemical dosage was 17%. In the flow-proportional chemical injection test, the system chemical concentration remained within 5% of the average value despite a fivefold range in water flow rates. With rising popularity of variable-rate application and increasing development of variable-rate chemigation equipment, the time is ripe for applied research and extension of variable-rate chemigation via center pivots.